Antigen-binding fragment (Fab) preparation is one of the most successful monoclonal antibody therapeutic agents. For example, Abciximab(ReoPro®), Ranibizumab(Lucentis®), and Certolizumab pegol(Cimzia®) etc. had already been approved as drugs in many countries. Furthermore, polyclonal Fab preparations including Abciximab(ReoPro®), Ranibizumab(Lucentis®) and Certolizumab pegol (Clmzia®) are commercially available in EU.
Conjugation of an exogenous effector domain may confer therapeutic effects to Fab fragments, when they form a Fab-effecter fusion format. Therefore, in fact, lots of antibody fragments in clinical development status are conjugated to an exogenous functional moiety. In such a Fab-fusion protein construct (or Fab-effector moieties construct), the antigen binding fragment may provide a target-specific delivery, and the fusion protein or (poly)peptide (effector domain) may provide therapeutic effects. Fusion domains originated from prokaryotic origin may include cytotoxins, for example, deBouganin (a de-immunized plant toxin) (see Entwistle et al., (2012) Cancer Biother Radiopharm. 27, 582-92), staphylococcal enterotoxin (SE) (see Ilack et al., (2003) Toxicology. 185, 161-174) or a mutant form of Pseudomonas exotoxin (see Choe et al., (1994) Cancer Res. 54, 3460-3467; see Kreitman et al., (1994) Int. J. Cancer 57, 856-864). In addition, fusion domains comprising polypeptides from eukaryotes, such as, scFv (see Lu et al., (2002) J Immunolog Meth. 267, 213-226) or cytokine (see Holzer et al., (1996) Cytokine. 8, 214-221; see Sjogaard et al., (1999) Int J Oncol. 15, 873-882), may function as therapeutics. Although radioactive isotope is chemically conjugated to Fab or (Fab′)2 fragment in general, cytotoxin, cytokine or enzyme is genetically fused to Fab or (Fab′)2. It is known that Fab molecules, unlike scFv, Fv or dsFv, can be produced with ease up to 1-2 g/L as a soluble form in the periplasm of E. coli (see Humphreys et al., J. Immunol. Methods. 209, 193-202; Carter et al., Biotechnology (N Y). 10, 163167; Venturi et al., J Mol Biol. 315, 1-8; Donzeau et al., Methods Mol Biol. 378, 14-31), or even in Pseudomonas fluorescens (see Retallack et al., Prot Exp Purif. 81, 157-165). Currently, lots of commercially available biological agents such as rhGH, insulin or various types of cytokines are being produced in E. coli (see Graumann and Premstaller, (2006) Biotechnol J. 1, 164-186; Chadd and Chamow, (2001) Curr Opin Biotechnol. 12, 188-194). In this regard, the genetic linkage of a therapeutic domain to a Fab fragment and other therapeutic agents has great advantage in the development of a new biological medicinal agent, and the improvement of the current biological drugs efficacy as well. Further, a Fab molecule might be fused with other antibody fragments such as scFv, Fv, dsFv or dAb to prepare bi-specific or tri-specific antibody molecule (see Lu et al., (2002) J Immunolog Meth. 267, 213-226). However, the expression of Fab-effector fusion proteins of which the effector is of eukaryotic origin in E. coli has been hampered because the effector domain could not be biologically functional due to inappropriate folding or the lack of glycosylation process in E. coli. Futhermore, the optimal fusion format to produce Fab-effector fusion proteins in E. coli periplasm has not yet been throughly studied. Most of serum proteins having molecular weight less than between 50 kDa and 60 kDa, such as, cytokines and growth factors, have a short half-life in vivo, for instance, from several minutes to several hours due to renal clearance. Thus, extending the serum half-life of therapeutic polypeptides or proteins is one of the most intensely studied areas in bio-pharmaceutical research (see Kontermann, (2012) Wiley, ISBN: 978-3-527-32849-9). For this purpose, various methods including pegylation, polysialylation, HESylation, glycosylation, or recombinant PEG analogue fused to flexible and hydrophilic amino acid chain (500 to 600 amino acids) have been developed (See Chapman, 2002; Adv Drug Deliv Rev. 54. 531˜545; Schlapschy et al., (2007) Prot Eng Des Sel. 20, 273˜283; Contermann (2011) Curr Op Biotechnol. 22, 868˜876; Jevsevar et al., (2012) Methods Mol Biol. 901, 233˜246). Furthermore, the FcRn-mediated recycling mechanism has been directly or indirectly employed in order to extend in vivo half-life of therapeutic proteins. Among serum proteins, it is known that a human serum albumin (HSA) and an immune globulin (in particular, IgG) have exceptionally a long half-life through the FcRn-mediated recycling mechanism. In a human body, the serum half-life of albumin is 19 days and that of an IgG molecule is between one week and almost 4 weeks depending on the subclass of IgG. Thus, these two molecules have been used as fusion partners to extend half-life of therapeutic proteins and/or (poly)peptides.
Recombinant hGH (˜19 kDa) prepared in cytoplasm or the periplasm of E. coli has been used in clinics to treat diseases caused by the lack of growth hormones in infants and adults as well, after in vitro folding process (see Blethen et al., (1997) J. Clin. Endocrinol. Metab. 82, 418-420). One major inconvenience in rhGH administration is the daily injection due to the short period of half-life (<30 minutes). To extend the serum half-life of hGH, chemical conjugation of polyethylene glycol (see Clark et al., (1996) J. Biol. Chem. 271, 21969-21977; Pradhananga et al., 2002 J Mol Endocrinol. 29, 1114; Cho et al., 2011; Sondergaard et al., (2011) J Clin Endocrinol Metabol. 96, 681-688), and chemical conjugation of the modified hGH to the arm of Fab of humanized CovX-Body IgG (see Palanki et al., (2013) Bioorg. Med. Chem. Lett. 23, 402-406) had been attempted. In addition, the elongation of the half-life of hGH in serum has been successfully achieved by the genetic fusion of human serum albumin (HSA) (Albutropin®) or the polypepeptide sequences comprising hundreds of Pro-Ala-Ser (PAS) residues (PASylation) (see Osborn et al., 2002 Eur J Pharmacol. 456, 149-158; Anderson et al., (2011) J Biol Chem. 286, 5234-5241; Sleep et al., (2013) Biochimica et Biophysica Acta. 1830, 5526-5534; Schlapschy et al., (2013) Protein Eng Des Sel. 26, 489˜501). The most well studied one in this category is VRS-317, a rGH genetically linked with XTEN amino acid sequences to the N-terminus and the C-terminus, which allows one month dosage regimen (see Schellenberger et al., (2007) Nat Biotech. 27, 1186-1190; Cleland et al., (2012) J Pharm Sci. 101, 2744-2754; Yuen et al., (2013) J Clin Endocrinol Metab. 98, 2595-2603). Also, hGH is associated with vascular disease (See Thomas J Merimee et. al., (1973), Diabetes, 22, 813-819) and CRETZFELDT-JAKOB disease (See John Powell-Jackson et al., 1985, Lancet, 2, 244-246). In addition, IFN-γ accelerates Graft-Versus-Host-Disease (See Bruce R.Blazar et. al., 2003, The Journal of Immunology, 171, 1272-1277) and IFN-α is related with autoimmune disease (See A Imagawa et al., 1995, The Journal of clinical endocrinology & metabolism, 80, 922-926). Also, GSCF is related with auto-immune disease (See Anke Franzke et al., 2003, Blood, 102, 734-739) and HCV associated with liver disease (See Van Thiel D H et al., 1995, Hepato-gastroenterology, 42, 907-912).
A Fab-fusion protein (or polypeptide) has a great potential as a therapeutic agent for treating chronical diseases which require a large dose of drugs for a long period of time, in particular, especially when the Fab-fusion protein can be produced in microorganism expression system with low cost. Despite such possible potent advantages of employing a Fab, however, there has been no attempt applying an anti-serum albumin (SA) Fab antibody in the development of a protein or a (poly)peptide drug having extended in vivo half-life. Herein, the inventors have completed the present invention by constructing a novel anti-serum albumin (SA) Fab-effector protein (or (poly)peptide) fusion constructs, and confirming the high-yield production of funtional fusion constructs in the periplasm of E. coli.